site/powerpc32-linux: Do not cache statvfs64 across glibc and musl

Newer version of musl does not expose LFS64 interfaces, therefore
caching this is not right thing to do across both glibc and musl
moreover we will enable largefile support on glibc too therefore caching
it here is redundant.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>